Characterization of new strains of Hortaea werneckii isolated from salt marshes of Egypt

Full Length Article

Characterization of new strains of Hortaeawerneckii isolated from salt marshes of Egypt

Ashraf Elsayed *, Amr M. Mowafy, Hoda M. Soliman, Ahmed Gebreil,Nada I. MagdyBotany Department, Faculty of Science, Mansoura University, Mansoura, Egypt

A R T I C L E I N F O

Article history:

Received 28 June 2016

Received in revised form 8

September 2016

Accepted 9 September 2016

Available online

A B S T R A C T

Three new black yeast strains (EGYNDA08, EGYNDA16 and EGYNDA90) of marine origin were

isolated from the Egyptian off shore salt marshes and molecularly identified by ITS1 and

ITS2 5.8S rRNA gene sequencing. The molecular identification showed a high sequence iden-

tity between the two of them and Hortaea werneckii Hw6 strain, while the other strain was

unique. The biochemical characterization using different nutritional media showed differ-

ent growth capabilities and the qualitative enzyme tests (such as catalase, urease, lipase,

proteases, amylases and cellulose) showed different activity levels. The morphological char-

acterization showed different developmental stages of hyphal maturation. The phylogenetic

analysis of the three strains indicated that, two isolates were evolutionary relevant to the

Hw6 strain isolated from Spain and one novel strain was isolated with rather different mo-

lecular and morphological characteristics.

© 2016 Production and hosting by Elsevier B.V. on behalf of Mansoura University. This is

an open access article under the CC BY-NC-ND license (http://creativecommons.org/

licenses/by-nc-nd/4.0/).

Keywords:

Black yeast

Hortaea and salt marshes

1. Introduction

From the taxonomic and phylogenetic point of view, ‘Black yeast’is a polyphyletic group [1,2] of dematiaceous, filamentous [3]fungi of which several representatives share morphological fea-tures [4] such as reproducing by unicellular growth [5]. Theythrive in extreme environments characterized by scarce nu-trients, low oxygen tension, high temperature, harmful UVradiation, osmotic stress as well as a mixture of these condi-tions [4].

Hortaea werneckii was identified as an extreme halotolerantfungus [6] that belongs to the black yeast group and was iso-lated from different marine habitats. H. wernrckii was reportedto inhibit the afore-mentioned extreme conditions. Hortaea sp.belongs to the Capnodiales order in the Ascomycota phylum[7]. Based on the state of the niche (static or dynamic) [5],H. werneckii switches between two main life phases yeast phaseand hyphal phase [8]. Both phases ended up with sclerotialbodies under sever environmental conditions [8].

Under light microscope, H. werneckii is a synanomorphic mi-croorganism which produces buds, conidia, arthrocondia and

* Corresponding author.E-mail address: [email protected] (A. Elsayed).

http://dx.doi.org/10.1016/j.ejbas.2016.09.0012314-808X/© 2016 Production and hosting by Elsevier B.V. on behalf of Mansoura University. This is an open access article under theCC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

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Please cite this article in press as: Ashraf Elsayed, Amr M. Mowafy, Hoda M. Soliman, Ahmed Gebreil, Nada I. Magdy, Characterization of new strains of Hortaea werneckiiisolated from salt marshes of Egypt, Egyptian Journal of Basic and Applied Sciences (2016), doi: 10.1016/j.ejbas.2016.09.001

Available online at www.sciencedirect.com

journal homepage: ht tp : / /ees .e lsevier.com/ejbas/defaul t .asp

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endoconidia. Buds are enteroblastic annellidic ones [8] and theyemerged as polar, lateral, and bipolar from yeast-like forms [9].Conidiogenesis and budding mode are the same as both budsand conidia are released by the complete separation of the de-veloped abscission line in a septum [3]. When cells aresuccessively generated from the same locus, the remnants ofthe outer layers of the cell wall are arranged consecutivelyaround the tip, an increase in neck (collars) of the mother cellresults in bottle-shaped cells marked by many rings directedtoward the pole and the number of rings is dependent on thenumber of buds or conidia released [8]. The conidia are pro-duced from the generative apex of annellidophores which areunbranched intercalary hyphal cells with tapered tips. Conidiaare mainly unicellular; however two-celled conidia separatedby conspicuous dark cross wall were found [3]. H. werneckii pro-duces hydrophobic dematiaceous septated mycelia [3] whichare formed of coherent thalli and extended from the mothercell wall [8] and lateral branches sometimes are expanded fromthem [9].

Hyphal cells septa have an abscission line separatingbetween septum sheets. In addition to the simple central pore,triangular points in mature cells are laying at the anastomo-sis of inner and outer layer which marks the future points ofseparation and the adjacent outer layer remains intact withouta separation line until releasing enteroarthric thin-walled scar-free cells either in the form of an endogenous conidia fromthe yeast-like cells or arthroconidia from the fragmentationof hyphae by shedding off parts of the outer cell wall layers,which are easily ruptured [8,9].

Up to our knowledge, isolation and characterization ofH. werneckii from the Egyptian environment was not reportedbefore. In this survey, the isolated strains of H. werneckii fromEgypt were molecularly, biochemically and morphologicallycharacterized to focus on differences between them andbetween other previously published characterized H. werneckiistrains.

2. Materials and methods

2.1. Sample collection

Water samples from different off shore salt marshes locatedafter 10 kilometers from west of Gamasa on Damietta road,were collected at the beginning of December and three samplesin the end of March. Samples were stored in glass sealed jars.

2.2. Isolation and purification of the marine black yeast

One milliliter from the collected samples was inoculated in twosaline enriched liquid medium (0.5% yeast extract without/with 1% glucose) dissolved in sea water and 100 μg/ml ofstreptomycin was added after sterilization in order to inhibitundesired bacterial growth. The incubation was held at 15 °C,25 °C and 30 °C in an orbital incubator shaker at 150 rpm forthree weeks [10].

After one week, sub-culturing from the liquid media of tur-bidity was performed on the same saline enriched agar media.Temperatures 15 °C, 25 °C and 30 °C were repeated until the

filamentous community invading during the first week and thendeveloped to unicellular communities appeared on the thirdweek until the appearance of yeast-like melanized colonieswhich are purified by sub-culturing on media containing 10%NaCl. The pure cultures were preserved in 20% glycerol andstored at −20 °C.

2.3. Molecular identification of the isolates

Fungal DNA was extracted by employing the FastDNA® SpinKit according to the supplier’s instructions.The yield of genomicDNA was measured by a Nano Drop spectrophotometer by mea-suring the absorbance at 260 nm. The ITS1 region from DNAsample extracts was amplified in triplicate using primers withhigh specificity for ascomycete fungi (18FITS1 (CTTGGTCATTTAGAGGAAGTAA) and 18RITS4 (TCCTCCGCTTATTGATATGC). ThePCR reactions were performed in a thermo-cycler at a totalvolume of 50 μl using the temperature programs: 94 °C for 5 min,94 °C for 40 s, 55 °C for 45 s, 72 °C for 1.5 min, 72 °C for 7 min(35 cycles). The sizes of the PCR products were determined byelectrophoresis on 1.5% agarose gels.The desired products wereexcised and purified by the Qiagen II Agarose Gel ExtractionKit.

The sequencing reactions were performed in a thermocycler(Master cycler, Eppendorf, Hamburg, Germany) at a total volumeof 10 μl by using the temperature program: 96 °C for 1 min, 96 °Cfor 30 s, 60 °C for 10 s, 60 °C for 4 min, 72 °C for 5 min (25 cycles).The sequencing reaction products were purified by employ-ing the Dye Ex 2.0 Spin Kit. The purified sequencing reactionproducts were dried in vacuum centrifuge and then analyzedusing applied biosystems (ABI PRISM Big Dye Terminator v1.1),Ready Reaction Cycle Sequencing Kit and employing an ABI3130 XL Genetic Analyser (Applied Biosystems, Darmstadt) [11].The obtained sequences were annotated using theSequencher™ 4.8 Software. DNA similarity searches were per-formed using the BlastN program and the databases ofEuropean Molecular Biology Laboratory (EMBL) and GenBankfrom the National Center for Biotechnology Information website(NCBI).

Phylogenetic and molecular evolutionary analyses for 18SrRNA gene nucleotide sequences were conducted for se-quence alignments using the computer programs ClustalW andBioEdit 7.0.5.3 and implement in MEGA software version 5. Phy-logenetic trees were constructed using the Neighbor-Joining [12]algorithm method. Distances were generated using the KimuraMatrix, and the tree stability was supported through Boot-strap analysis (1000 replications).

2.4. Biochemical characterization

2.4.1. Nutritional characteristicsDifferent media were tested for supporting the growth of theisolates such as Malt Extract Agar media (MEA) (2% malt extractand 1.5% agar) [2], Potato Dextrose Agar media (PDA) (2% dex-trose 20 g, sliced potato 1.5% agar) and modified Yeast ExtractPeptone Dextrose media (YPD) (2% glucose-1% pepton-1% yeastextract-1.5% agar) [13]. All media were dissolved in sea waterand cultures were incubated at 25 °C.

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2.4.2. Enzyme tests

2.4.2.1. Catalase test. In room temperature, a drop of diluted30% Hydrogen Peroxide was placed onto a slide containing adrop of liquid modified YPD containing tested organisms with6 days old. Effervescence reaction could be observed in-stantly as a positive result [14].

2.4.2.2. Urease test. Rustigian and Stuart’s urea broth media[15] containing urea 20 g, monopotassium phosphate 9.1 g, di-potassium phosphate 9.5 g and Phenol Red 0.01 g were dissolvedin one liter of distilled water with final pH 6.8, were sterilizedusing Millipore filter papers, poured into sterilized tubes, in-oculated with culture and incubated at 25 °C for five days. Thechange in media color from yellow to pink was regarded as apositive result.

2.4.2.3. Lipase test. Sierra lipase test protocol was done [16]using Tween-80 (10.0 g) and agar 20.0 g in one liter of sea waterand the final pH was 6. Agar was dissolved in sea water andautoclaved and Tween was sterilized separately. After inocu-lation, the plates were incubated at 25 °C for three days. Theobservation of white precipitation around the growinginoculums was considered as a positive result.

2.4.2.4. Proteases test. A modified protocol of 30% skim milk-agar medium [17] was done by adding 30 ml packed liquid skimmilk (the used skim milk nutrition label on the pack: Fats .44 g,Carbohydrates: 10.6 g, Protein: 6.9 g, Vitamin: B1 .1 mg andVitamin: B2 .14 mg). The formation of transparent zone aroundthe growing isolates was considered as a positive result.

2.4.2.5. Amylases test. Vedder starch media composed ofsoluble starch 10 g, agar 12 g and sodium nitrate 6.5 g were dis-solved in one liter sea water and adjusted to pH 6. Amylasesactivity was detected by flooding the surface of inoculatedmedia with Grams Iodine [18].

2.4.2.6. Cellulase test. The Carboxymethylcellulose (CMC) media[19,20], which were composed of: CMC 10 g, Sodium Nitrate 6.5 g,Potassium Hydrogen Phosphate 6.5 g, Potassium chloride 6.5 g,Magnesium sulphate heptahydrate 3.0 g and Agar 17.5 g in oneliter with final pH of 6, were used for cellulose activity. The ac-tivity was visualized by staining the media with Congo red dyefollowed by de-staining with Sodium Chloride solution. De-

staining process was repeated continuously until a clear zoneappeared around the growing hyphae.

2.5. Microscopic characterization

Specimens of the three strains of the five days old light greencolonies for yeast phase formation and one month old blackcolonies for hyphal phase formation were examined under lightmicroscope (40×).

3. Results

3.1. Black yeast isolation

The incubational temperature 25 °C and 10% NaCl enhancedthe growth of the black yeast isolates. Two isolates were re-covered from water samples, EGYNDA08 at the beginning ofDecember and EGYNDA16 at the end of March, while anotherisolate EGYNDA90 was recovered from NaCl crystals of saltmarshes at the beginning of May.

3.2. Molecular identification

From the phylogenetic tree (Fig. 1), three new black yeast strains(EGYNDA08, EGYNDA16 and EGYNDA90) were visualized. Oneof them (EGYNDA90, accession number KU341734) lay in a sepa-rate branch while the others, EGYNDA08 (accession numberKU341732) and EGYNDA16 (accession number KU341733), werevery close to each other and to Hw6-JN997370.1 which was iso-lated from Spain. The similarity between EGYNDA16 and theother ecotypes was 97.4% maximum using Pairwise SequenceAlignment (Table 1).

3.3. Biochemical characterization

3.3.1. Nutritional characteristicsEGYNDA08 grew on MEA as black small colonies with hyphalgrowth stimulation; also it grew on the modified YPD media,meanwhile, EGYNDA16 and EGYNDA90 grew on YPD media andthey hardly grew on MEA and the media contained 0.5% yeastextract.

3.3.2. Enzymes tests

3.3.2.1. Catalase test. The effervescence that resulted on a slidewas very weak in case of EGYNDA08, very strong in case of

Fig. 1 – Phylogenetic tree constructed by MEGA using Neighbor-Joining tree, with number of Bootstrap replications 500,between different Hortaea werneckii strains including the three isolates and Phaeotheca triangularis. T = ex-type strain.

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EGYNDA16 and almost intermediate in case of EGYNDA90(Fig. 2A).

3.3.2.2. Urease test. In case of EGYNDA08, the color change fromyellow to pink was sharper than that in case of EGYNDA90 in-

dicating higher urease activity, while, the lowest activity wasrecorded for EGYNDA16 (Fig. 2B).

3.3.2.3. Lipase test. White precipitate appeared around all theisolates (Fig. 2C) indicating the lipase activity for all.

Table 1 – Sequence homology of the 18S rRNA gene of H. werneckii isolates from the salt marshes with yeast isolatesfrom public data bases.

Isolate Accession number Closely related yeast Homology (%) Size (bp)

EGYNDA08 KU341732 H. wernechii 6-JN997370 100 501EGYNDA16 KU341733 H. wernechii 6-JN997370 97.4 471EGYNDA90 KU341734 H. wernechii 6-JN997370 100 459

Fig. 2 – Enzyme tests results. (A) Positive results of catalase test, (B) positive results of urease test, (C) positive results oflipase test, (D) positive results of proteases test, (E) positive results of amylases test and (F) positive results of cellulase test.

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3.3.2.4. Protease test. Hydrolysis of proteins around colonieswas achieved by the three isolates (Fig. 2D) indicating prote-ase activity for all the isolates.

3.3.2.5. Amylase test. Clear zone around colonies was achievedby the three isolates (Fig. 2F) indicating the ability for all of themto degrade starch.

3.3.3. Microscopic characteristicsGenerally, the isolated strains have all morphological fea-tures recorded previously to other H. werneckii strains andmentioned briefly in the introduction. Table 2 summarizes themorphological differences among the isolated black yeast

strains. EGYNDA08 was studied as a model for the develop-mental stages of hyphal maturation. Newly developedhyphae appeared as non-septated coenocytic thin hyphae(Fig. 3D1).

Polar septum formation started from the older parts of thefilaments at the colony base and continued to the tip of thefilaments and the intercalary cells become wider by age andfollowed by conidiogenesis (Fig. 3D2). Two weeks old fila-ments terminated conidiogenesis and intercalary cells startedto divide leading to the irregular size and shape of cells. Frag-mentation has also been noticed in old filaments (Fig. 3D3) thensclerotial elements production was the final step in the cycle(Fig. 3D4).

Table 2 – Morphological characteristics of H. werneckii strains isolated from salt marshes.

Characteristic Strain

EGYNDA08 EGYNDA16 EGYNDA90

Cell length 5.2–7.8 μm 5.2–46.8 μm 5.2–20.8 μmCell width 2.6–5 μm ~2.6 μm 2.6–5.2 μmSpherical cells Not present 10.4 μm 6.5–7.8 μmCell description Two-celled pattern, conspicuous and heavily

melanized thick septum and cell wall. (Fig. 3A).Melanosomes were low in numbers and large insize, they were located inside and outside thecell (Fig. 3B1), anastomosis triangles in septumare pigmented (Fig. 3B2).

Two shapes of cells: rod andspherical (Fig. 4A). Cell wall,septum and melanization wereweak (Fig. 4A). Many finemelanosomes.

Cell wall and septum weremedium in thickness andmelanizationMelanosomes were many andfine (Fig. 5A).

Hyphal development Short mucilage Rare, if present, zigzag non-septated (Fig. 4C).

Zigzag coenocytic (Fig. 5B). Long,albino aerial mycelium (Fig. 2D).

Budding style Polar (Fig. 3C1), sided polar (Fig. 3C2), bipolar(Fig. 3C3) and sympodial (Fig. 3C4)

Mainly polar and other styleswere rare

Mainly polar and other styleswere rare

Annellidic ring Few rings max. 3 (Fig. 3D2) Many rings (Fig. 4B1, B2 and B3). Medium number of rings

Fig. 3 – EGYNDA08 isolate under light microscope (40×). (A) The most frequent morphological characteristics (two-celledpattern, conspicuous septa and melanized cell wall. (B1) Bold arrows showing the cytoplasmic melanosomes aggregatedinside and outside the cell. (B2 and B3) Light arrows referring to the accumulation of melanin position. (C1–C4) Differentstyles of budding cells (C1) polar, (C2) sided polar, (C3), bipolar (C4) sympodial. (D1–D4) Filaments at different ages. (D1) Fivedays old hyphae, (D2) ten days old hyphae, arrows are pointing to annellidophores, (D3) twenty days old petri-dish boldarrow pointing to fragmented filament and double-headed arrow is pointing to the same number of vesicles inside twocells and inside fragmented hyphae, (D4) one month old culture with irregular sclerotial elements.

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4. Discussion

The biggest obstacle to the halophilic black yeasts study is notlaying in extreme conditions but in their inability to prohibitthe invasion of other competing microorganisms that is similarto the behavior of the acidophilic fungi [21]. Additionally, iso-lating H. werneckii was a big challenge [4] because a successfulpurification depends on choosing the unsuitable isolation con-ditions to other fungi contaminating the sample and in thesame time tolerable by the organism of interest such as highsalt concentration in media [4], high pH >9 and low tempera-ture <20 °C. Media type, temperature and media state affectedthe examined shape and the stages of Hortaea cells under mi-croscope, even the temperature in which they are growingaffected the relativity between hyphal and yeast phase. Yeast

phase was more frequently observed and could be describedas the dominant phase at low temperatures (15–20 °C), however,hyphal phase was the dominant phase at high temperatures(25–30 °C). When a four-day-old colony was picked and exam-ined by light microscope, it showed the different growth phasesexcept the sclerotial bodies. On the other hand, the isolatesexamined from the liquid media were much more homog-enous cells with almost the same shape and size.

Morphological differences were observed and recorded bycareful comparison between the three isolates cultivated underthe same laboratory conditions to avoid the gradual changeand loss in the unnecessary morphological characteristics ofthe tested lab organisms over the research study period.

The general environmental or controlled conditions sur-rounding black yeasts are majorly responsible for sculpturingtheir morphological identity so culturing the organisms re-peatedly in controlled conditions probably leads to differentphenotype. As an example, EGYNDA16 was rarely observed toproduce filaments until it was cultured repeatedly on solidmedia at which wide spaces between spots were consideredindicating that the laboratory conditions and the cultivationmethod forced the cultured organism to produce hyphae whichmight be necessary for the organism to obtain nutrients.

The yeast-like pattern gave a wide variety in budding styles:polar and sided polar budding (Fig. 3C1 and C2) which was trig-gered by growing on solid media may be when cells on thesurface of colony were budding vertically downward then hori-zontally outward. Bipolar budding (Fig. 3C3) maybe due tonuclear division occurrence in one mother cell and each nucleiordered its half with budding from each pole before a sepa-rating septum is formed. Sympodial budding (Fig. 3C4) wastriggered in old cultures. Hyphal branches’ irregularity has beenmentioned as a cause to prolonged culturing of the organismin liquid culture [22]. The characteristic shape of zigzag hyphaehas been noticed in Ashbya gossypii and the dimorphic patho-genic fungus Histoplasma capsulatum as the studies proved thatthe hyphae shape might be affected with calcium availabilityin surrounding media [23] or calcium binding protein gene mu-tation [24].

Fig. 4 – EGYNDA16 isolate under light microscope (40×). (A) Black bold arrows are pointing to big cells while thin arrows arepointing to long cells. (B1–B3) Annellidic budding and brackets are referring to annellidic conidiogenesis, arrows arepointing to the original cell (B3) which was potential for shedding off endoconidia. (C) Isolated hyphaea from broth media.

Fig. 5 – EGYNDA90 isolate under light microscope. (A) Blackbold arrow is pointing to a relatively big cell while thinarrow is pointing to long cells. (B) Zigzag-shaped branchedhyphae growing on the figure after few days; filament isstraightened once it gets septated.

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It could be concluded that new black yeast strains have beenisolated and characterized in this study.They all have been iden-tified as H. werneckii, two of them EGYNDA08 and EGYNDA16were ecotypes of each other and EGYNDA90 lay in a separatebranch. Up to our knowledge, this is the first report describ-ing the occurrence of this organism in Egypt.The isolates showdifferences in morphological characteristics as described in theresults and the enzymatic assays showed qualitative differ-ences. Further studies are ongoing to verify the pleomorphiccharacterization and the adaptation mechanism of these iso-lates to the saline habitat they could survive.

Acknowledgments

Many thanks to Prof. Samia Ali Haroun, the former head ofbotany department, Faculty of Science, Mansoura University,Egypt and many thanks to Prof. Heshmat Soliman Aldesuquythe current head of the department for their valuable help andencouragement. We thank Dr. Eladl Gala from the same de-partment for his continuous support and valuable discussions.

R E F E R E N C E S

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[8] de Hoog GS, Gerrits van den Ende AH. Nutritional patternand eco-physiology of Hortaea werneckii, agent of humantinea nigra. Antonie Van Leeuwenhoek 1992;62(4):321–9.

[9] Mittag H. The fine structure of Hortaea werneckii. Mycoses1993;36(11–12):343–50.

[10] Gunde-Cimermana N, Zalarb P, de Hoogc S, Plemenitasd A.Hypersaline waters in salterns – natural ecological nichesfor halophilic black yeasts. FEMS Microbiol Ecol2000;32(3):235–40.

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[12] Muzyka D, Pantin-Jackwood M, Stegniy B, Rula O, Bolotin V,Stegniy A. Wild bird surveillance for avian paramyxovirusesin the Azov-black sea region of Ukraine (2006 to 2011)reveals epidemiological connections with Europe and Africa.Appl Environ Microbiol 2014;80(17):5427–38.

[13] Kejzar A, Gobec S, Plemenitas A, Lenassi M. Melanin iscrucial for growth of the black yeast Hortaea werneckii in itsnatural hypersaline environment. Fungal Biol2013;117(5):368–79.

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[16] Sierra G. A simple method for the detection of lipolyticactivity of micro-organisms and some observations on theinfluence of the contact between cells and fatty substrates.Antonie Van Leeuwenhoek 1957;23(1):15–22.

[17] Kazanas N. Proteolytic activity of microorganisms isolatedfrom freshwater fish. Appl Microbiol 1968;16(1):128–32.

[18] Vedder EB. Starch agar, a useful culture medium. J Infect Dis1915;16(3):385–8.

[19] Stewart JC, Stewart CS, Heptinstall J. The use of tritiatedcellulose in screening for cellulolytic microorganisms.Biotechnol Lett 1982;4(7):459–64.

[20] Shahriarinour M, Mohd Noor A, Ariff A, Mohamad R.Screening, isolation and selection of cellulolytic fungi fromoil palm empty fruit bunch fibre. Biotechnology2011;10(1):108–13.

[21] Selbmann L, de Hoog GS, Zucconi L, Isola D, Ruisi S, van denEnde AH. Drought meets acid: three new genera in adothidealean clade of extremotolerant fungi. Stud Mycol2008;61:1–20.

[22] Takeo K, De Hoog G. Karyology and hyphal characters astaxonomic criteria in ascomycetous black yeasts andrelated fungi. Antonie Van Leeuwenhoek 1991;60(1):35–42.

[23] Bauer Y, Knechtle P, Wendland J, Helfer H, Philippsen P. ARas-like GTPase is involved in hyphal growth guidance inthe filamentous fungus Ashbya gossypii. Mol Biol Cell2004;15(10):4622–32.

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Documents

Characterization of new strains of Hortaea werneckii isolated from salt marshes of Egypt